Non-oriented silicon steel is mainly used to make the stator cores of medium and large-sized motors (>50 HP) and generators, as well as the stator and rotor cores of small-sized motors with high requirements on energy efficiency. In order to miniaturize electronic equipment and conserve energy, it is required that the non-oriented silicon steel used should be of low iron loss and excellent anisotropy of iron loss.
The traditional method for manufacturing the non-oriented silicon steel adopts the casting slab containing silicon (2.5 wt % or more) and aluminum (0.2 wt % or more) to increase the electric resistance of the non-oriented silicon steel, thus reducing its iron loss. However, the method requires a final annealing temperature of 1,000° C. or more, which results in the problems of high cost, nodulation of furnace roller, etc.
In order to manufacture the non-oriented silicon steel which can both miniaturize electronic equipment and conserve energy, many studies have been conducted on the ingredients and manufacturing process of non-oriented silicon steel, with the purpose of developing the non-oriented silicon steel with excellent magnetic properties.
The U.S. Pat. No. 4,560,423 discloses a casting slab containing the following ingredients as calculated by weight percentage: Si≥2.5%, Al≥1.0%, 3.5%≤(Si+Al)≤5.0%, S≤0.005% and N≤0.004%, which goes through the two-stage annealing process, i.e., it is firstly kept thermal insulation at 850˜1,000° C. for 30˜120 s and then at 1,050° C. for 3˜60 s to obtain the non-oriented silicon steel having an iron loss of P15/50≤2.70 W/kg (silicon steel of 0.5 mm thickness).
The Japanese published Patent JP1996295936S discloses a casting slab containing the following ingredients as calculated by weight percentage: C<0.005%, Si: 2.0˜4.0%, Al: 0.05˜2%, Mn: 0.05˜1.5%, P≤0.1%, S≤0.003%, N≤0.004%, Sn: 0.003˜0.2%, Cu: 0.015˜0.2%, Ni: 0.01˜0.2%, Cr: 0.02˜0.2%, V: 0.0005˜0.008% and Nb<0.01%, which goes through the normalizing and cooling process at cooling rate of 80° C./s or less, then the cold rolling process at the reduction rate of 88% or more and finally the two-stage annealing process to obtain the non-oriented silicon steel having low iron loss.
In the U.S. Pat. No. 6,139,650, Sb, Sn and rare earth elements such as Se, Te are added into the casting slab to control the S content, the surface nitrogen content and the like of the silicon steel, and thus to control iron loss P15/50 of silicon steel (silicon steel of 0.5 mm thickness) to be 2.40 W/kg or less.
Although all the above prior technologies can control the iron loss of silicon steel at a relatively low level, they have not taken into account the anisotropy of iron loss. It is well known that, the anisotropy of iron loss of silicon steel directly influences the rotational loss of stator and rotor cores and is one key factor determining the excellent loss characteristic of motor-driven equipment. Therefore, development of the non-oriented silicon steel simultaneously having low iron loss and excellent anisotropy of iron loss will present an important significance and broad application prospect.